The field of the present invention relates to the use of treated polyethylene terephthalate (PET) polarizing films in optical-quality plastic parts.
A variety of polarizing films is known to exist. Conventional polarizing films, however, have not been comprised of PET. This fact is primarily due to PET""s inert properties. The use of PET polarizing films in optical-quality polarized parts, as disclosed in the parent application, is therefore a unique innovation. Moreover, as disclosed in the parent application, such polarized parts can include ophthalmic lenses (semi-finished or finished prescription or non-prescription blanks, lenses, goggles, visors, shields), polarized facemasks or shields, and polarized display devices or windows that require low haze.
When a polarizer is incorporated in an optical-grade plastic part, it is difficult to effect secure and consistent adhesion of the total construct. Part of this difficulty can be attributed to the environmental instability of the conventional polarizer (polyvinyl alcohol polarizers, for instance, are sensitive to heat and humidity exposure). While polarizer stability is markedly improved by using PET polarizing film as disclosed in the parent application, the concern with separation between the polarizer and the rest of the plastic matrix remains. In fact, given the recognized inertness of PET, secure and consistent adhesion may be even more problematic.
Conventional techniques of incorporating a polarizer into an optical-grade plastic part have included the use of adhesives. However, placing adhesive on the polarizer film to secure it in the plastic matrix can lead to surface irregularities that compromise optical quality as well as bonding integrity. High temperature or humidity exposure, as well as the additional grinding, polishing and edging processes often associated with optical parts may weaken these bonds. In addition, adhesive layers are thick enough (0.5-10 xcexc) to cause optical interference effects. These effects may include scattering within the layers that leads to unacceptable haze of the part, and refractive index mismatches that can cause interference fringing, image distortion, or chromatic aberration.
Nonetheless, there may be instances where one wants to secure a stable polarizer to an existing optical plastic by adhesively bonding it to a solid surface. The embodiments disclosed herein may therefore be beneficial for adhesively-bonded constructs because a) one uses the more environmentally stable PET-type polarizer film, and b) one can increase the bond strength between the adhesive and the inert PET surface by treatment geared to enhanced chemical bonding.
In the search for more stability with conventional polarizers, one approach has been to create a protected film by sandwiching the film between two layers of more robust optical plastics. Again, this construct suffers from the problems of bonding with adhesives. In addition, two more discrete layers of plastic within the optical-parts construct add four more surfaces for possible delamination, haze, and other optical-surface losses.
Another significant problem with the xe2x80x9csandwichxe2x80x9d approach is that the construct cannot be radically curved without causing creases, folds, or unacceptable optical deformation. However, many optical applications require highly curved spherical, cylindrical, or multi-dimensionally curved surfaces. Examples range from wrap-around sunglasses to motorcycle or ski visors and face shields to curved device displays.
A thin but environmentally stable polarizing film that can be reproducibly positioned in or on an optical-quality plastic part would offer a distinct advantage. However, the adhesion between the polarizer film and the optical polymer must be excellent to accommodate likely events that would lead to delamination in highly curved parts. These likely events include pre-or post-shaping of the film/polymer construct; frame tensions at unusual angles; grinding, polishing, and edging stresses of a steeply or non-uniformly shaped part; and non-uniform stress distributions within a highly curved or non-uniformly shaped parts when subjected to thermal or other environmental changes.
In addition, it may be desirable to overcoat these optical parts for increased physical or optical performance. Common coatings include scratch or abrasion-resistance layers, anti-reflection coatings, mirrored coatings, and anti-fogging layers. Similar to the bond between the polarizer film and the optical part, it is again imperative that excellent adhesion between the polarizer film and the overcoat is achieved to ensure product integrity during use, or during post-processing steps such as shaping, grinding, or edging the part.
Accordingly, a surface treatment that changes the physical and/or chemical nature of the PET polarizing film for improved adhesion to optical-quality plastics, as well as to subsequent coatings, is desired. Preferably, this change should not be so transitory that reversion to the pre-treated, less-bondable surface properties occurs within normal manufacturing cycle times. More preferably, as a treated film may be stored for an extended time (days to weeks) before being placed within a plastic part, this change should not be so transitory that reversion to the pre-treated, less-bondable surface properties occurs within the stored duration. In addition, advantageous effects gained by the surface treatment should not be vitiated by any deleterious effects that may reduce the polarization properties of the film. Such deleterious effects to be avoided include chemical or physical changes to the film that can cause surface distortions that reduce the optical quality of the film and the resulting optical plastic part.
The preferred embodiments relate to an optical-quality plastic part construct having a PET polarizing film integrally bonded thereto and, optionally, a hard coating integrally bonded to the PET polarizing film after it has been bonded to the optical construct. As an added benefit, utilizing the techniques of the preferred embodiments disclosed herein, one may advantageously place the polarizer on or near the surface of the construct either by strengthened adhesive bonding or by positioning the polarizer at the front surface during the molding process without the degradation concerns inherent with the use of conventional polarizers.
In a preferred construction, the PET film is surface treated, either physically and/or chemically, for integrally bonding the film to the optical plastic material. One preferred embodiment involves changing the surface characteristics of one side of the PET film for improved adhesive bonding to existing optical plastic parts. Another preferred embodiment involves changing the surface characteristics of one side of the PET film for improved bonding to thermoplastic polymer mixes molded against the treated surface of the film.
Similarly, in another preferred construction, the PET film is physically and/or chemically surface treated for integrally bonding to a coating, such as a hard coating. Various other embodiments may utilize some but not all of the above elements, or may include additional refinements, while obtaining the benefit of an optical-quality plastic part utilizing PET film.